Scientists have revealed that a new sperm separation technique could one day allow future parents undergoing IVF to choose whether to have a boy or a girl before fertilization.
And is that a team of Japanese researchers has published in the journal PloS Biology a new method that allows them to separate sperm from mice with an X chromosome from those with a Y chromosome, which means that sperm can be selected based on whether they will produce female (XX) or male (XY) offspring to fertilize an egg.
The experts state that they made their discovery as part of a project to discover and understand the differences between sperm that carry an X chromosome or a Y chromosome, noting that the former carries many more genes than the latter.
“This is the first study to scientifically show the functional differences, that is, the ability to fertilize, between sperm X and sperm Y,” says Masayuki Shimada, a co-author of the research from the University of Hiroshima.
As they state,your work could also prove useful in agriculture.“On a dairy farm, the value of a female dairy cow is much higher than the male, because milk is only produced by female cows,” says Shimada. “In the case of beef production, the growth rate is much higher in males after castration than in females.”
Although there are already methods such asflow cytometrythat can be used to classify sperm, these are based on the relative size of the X and Y chromosomes and are expensive. Rather, the latest findings are based on differences in the movement of the two types of sperm, which the team suggests may be a cheaper and simpler technique.
Scientists exploited the fact thatX chromosomes have many more genes than Y chromosomes,so they can produce a different range of proteins, including certain receptors that can bind to specific substances. The team focused on two of these receptors, called TLR7 and TLR8. They both join a drug calledResiquimod, an antiviral and antitumor agent. They found that when they exposed the sperm of the mice to a solution containing this drug, the velocity of some of the sperm was suppressed. The drug also reduced the percentage of sperm that, when placed in a test tube, swam into a layer rich in nutrients.
As expected, the drug was specifically affecting sperm that carried an X chromosome; the process did not harm sperm or their ability to fuse with an egg . In this way, this method could be used to distort the odds of male and female offspring in mice, they thought.
When testing his theory with rodents, 83% of the mouse pups were male. When samples enriched for X chromosome sperm were used for fertilization, most of the embryos were XX and more than 80% of the pups born were female.
Shimada said the process may be applicable to humans and other species if the receptors are found to be present on human sperm. The team acknowledges that the possibility of using the technique in humans raises ethical problems, although these are not new.
Expert feedback
Professor Robin Lovell-Badge, an expert in developmental biology at the Francis Crick Institute in London, said the research could prove very useful if similar effects are seen in farm animals. He added that it may also help solve the riddle of why, even in nature, the sex ratio in some mammals drifts away from 50:50 under certain environmental conditions, noting that there is evidence that in humans stress can have that effect.
“While the mice that were born after sperm sorting appeared normal, it would be essential to check for long-term effects of activating these receptors before fertilization. In other words, don’t try this at home in an attempt to skew the probability of having a boy or a girl. “
James Turner, who heads the sex chromosome biology lab at the Francis Crick Institute and was not involved in the study, commented:
“X and Y sperm carry different sex chromosomes, but they must share the proteins produced by these chromosomes to develop normally. This exchange means that no specific X or Y sperm markers have been found, which in turn has hampered attempts at sexual sperm. The authors report that X-chromosome TLR proteins escape the sharing rule, are found only in X sperm, and experimentally exploit TLR biology to isolate X- from Y sperm and generate litters of mice that are predominantly of a sex. The discovery of a protein that only X sperm marks is truly surprising, so the top priority will be to reproduce this finding and understand why this protein is the exception to the rule. It is not clear whether the TLR protein escapes the sharing rule in other animals. Resolving this point would be essential before the technique could be applied in other settings, for example in the dairy industry, where an excess of females is required. “
Allan Pacey,Professor of Andrology at the University of Sheffield, said:
“There have been many attempts over the years to develop techniques to separate the sperm that contain X and Y chromosomes and thus influence the sex of farm animals (for commercial purposes) or humans (for social reasons). We also know that nature is quite ingenious in how it can influence the sex of born offspring in response to specific environmental or social conditions. However, to date, the mechanism by which it does so is poorly understood. Therefore, this document is very interesting because it highlights the inherent physiological differences between X and Y sperm in the laboratory. The experiments reported are very elegant and show that by manipulating just two molecules on the surface of the sperm it is possible to drastically change the rate at which sperm with X or Y can swim. The authors propose that this works by altering the amount of energy produced by the do s types of sperm. This in turn allows for the collection of X- or Y-enriched sperm populations that, when used in IVF, can skew the ratio of male to female mouse pups born. “
“However, to date, experiments have only been done on sperm from laboratory mice and we don’t know if this effect would be seen on sperm from other animals, such as cattle (where producing more females is important for dairy herds)) or in humans where the parents might want a child of a specific sex. However, the data suggests that sperm cells are much more complex cells than we have previously known and that we still have much more to learn about them. ” , concludes the expert.
Referencia: Takashi Umehara, Natsumi Tsujita, Masayuki Shimada. Activation of Toll-like receptor 7/8 encoded by the X chromosome alters sperm motility and provides a novel simple technology for sexing sperm. PLOS Biology, 2019; 17 (8): e3000398 DOI: 10.1371/journal.pbio.3000398
